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Nov. 10, 2008 (New Orleans) -- If you have a pacemaker or an implantable cardioverter defibrillator (ICD), do not take your mp3 headphones out of your ear and drape them in front of your chest.

So advise doctors who found that headphones placed within an inch or so of these devices may cause them to misfire.

The research was presented at the American Heart Association's (AHA) Scientific Sessions 2008.

Earlier this year, the FDA said that interactions between mp3 players and similar digital music player devices, such as the iPod, and implanted cardiac devices are unlikely to occur.

"But we wanted to look at whether the headphones -- not the players, themselves -- would interact with implanted cardiac devices," says William H. Maisel, MD, director of the Medical Device Safety Institute at Beth Israel Medical Center in Boston.

That's because virtually every speaker contains magnets. "They are what vibrate and make sound," Maisel tells WebMD. "Portable headphones, because they are so small, need concentrated magnets."

Magnets and Heart Devices

Typically, doctors use magnets to ensure that pacemakers, which treat irregular heart rhythms, are working properly. When exposed to a magnet, the devices pace at a predetermined rate, Maisel explains.

"But when exposed to the concentrated magnet in a headphone, the patient can temporarily feel palpitations."

ICDs, which treat dangerously fast heart rhythms, send either low- or high-energy signals to the heart to abolish them. If ICDs are exposed to concentrated magnetic fields, they may temporarily stop looking for abnormal heart rhythms.

For the new study, the researchers tested eight different models of mp3 player headphones, including both the clip-on and earbud variety, with iPods on 60 defibrillator and pacemaker patients.

"We placed the headphones on the patients' chests, directly over where their devices are located, monitoring them for evidence of an interaction," Maisel says.

There was detectable interference with the device in 15% of the pacemaker patients and 30% of the defibrillator patients. Clip-on headphones were more likely to cause device interference than earbud models.

AHA spokesmanKenneth A. Ellenbogen, MD, of Virginia Commonwealth Medical University in Richmond, stresses that interruption of heart function is only temporary. Removal of the headphones restores normal device function.

"Plus, it wouldn't be typical to have headphones within an inch of the device," he tells WebMD.

Maisel agrees. "Just keep you headphones at least 3 centimeters, or 1.2 inches, from your implantable devices -- that is, do not place headphones in a front shirt pocket or drape them over your chest."

"And make sure a family member wearing headphones doesn't rest his or her head right on top of your device," he adds.